The present invention relates to a method for assessing the deterioration of motor oil.
Software-based systems for indicating the necessity of an oil change in motor vehicles are conventional. Some of these systems are based on algorithms which evaluate parameters such as the kilometers driven since the last oil change or the frequency of cold starts.
Alternative conventional methods use sensor signals which directly describe the physical condition of the oil. Appropriate sensors may measure, for example, the dielectric constant of the oil or the oil viscosity. In this context, a viscosity-based oil-change criterion may be derived from the determination of the viscosity change in the motor oil since the last oil change, since motor oil deterioration may be associated with an increase in the viscosity value. An evaluating electronics having an associated display device may store, for example, a viscosity threshold value, which is compared with the measured viscosity values of the motor oil. The vehicle driver may be provided with an indication regarding the impending necessity for the next oil change when the viscosity threshold value is exceeded.
The physical oil parameters measured using conventional methods are generally temperature-dependent, so that, to determine a comparison value, a temperature-compensation calculation is necessary.
In conventional methods for determining the oil viscosity, because the engine is in operation, a large part of the oil medium to be measured is in circulation. Therefore, it is not always possible to sufficiently wet the oil-viscosity measuring sensor, which may result in measuring errors.
The exemplary method according to the present invention may have the advantage that, as a result of the simultaneous determination of the oil temperature using a temperature sensor that is assigned to the sensor for measuring the oil viscosity, it is possible to reliably record a viscosity-temperature characteristic curve. A further evaluation variable may be available for evaluating the oil condition using the viscosity index that is characterized by the temperature-viscosity curve. In addition, the exemplary method according to the present invention, as a result of measuring the oil viscosity and the oil temperature in the cooling phase of the engine after it has been switched off, may have the advantage that the measurements can be carried out within a relatively large temperature range (assuming ambient temperatures in the area of about 25xc2x0 C. and operating temperatures of the motor oil in a range of up to about 150xc2x0 C.). A measuring temperature range of this type occurs during the warm-up phase of the motor oil, although the above-mentioned disadvantages such as insufficient wetting of the measuring sensor(s) may occur as a consequence of the motor being in operation.
The control of the oil-temperature and oil-viscosity measurements as well as the storing and evaluating of the measuring results obtained can be accomplished according to an exemplary embodiment of the present invention by an engine control unit assigned to the engine. This may offer the advantage that, for carrying out the exemplary method according to the present invention, no special control electronics may be necessary, because conventional engine control units are still in operation even during a so-called slowing-down time after the engine is switched off. This slowing-down time can be up to about 30 minutes, so that it may be advantageous to carry out the measurements of oil temperature and oil viscosity in a time interval of up to about 100 minutes, possibly from about 10 minutes to about 30 minutes after the switching-off of the engine. In this manner, numerous measuring values may be produced, which may make possible a sufficiently precise viscosity-temperature characteristic curve for the assessment of the deterioration of the motor oil.
It may also be expedient to assign the evaluation to a computing device that is arranged in the instrument panel, which may result in a further reduction in the components. Alternatively, it may be possible to integrate the evaluation in the engine control unit. Because the oil-viscosity and oil-temperature measuring values may be determined and their subsequent evaluation is carried out after the engine has been turned off, sufficient computing capacity may be present for the evaluation of the measuring values, in contrast to evaluation times while the engine is in operation. In response to the next commencement of travel, the measuring values obtained may be conveyed to the vehicle user by the display device assigned to the evaluating electronics. Because the condition of the motor oil may change only slightly during a single journey, conveying oil-condition information outside of xe2x80x9creal-time operationxe2x80x9d may be unproblematic.